Centrifugal compressors have existed for many years, and there exist many different designs. Historically, compressed air (or a gas/air mixture) has been generated by various types of motor driven machines. To achieve high efficiency, the motor must drive the centrifugal compressor at high rotational speeds. As rotational speeds become greater the overall machine size can be made smaller, while maintaining the same compressed air flows, pressures, and motor power. However, requirements for running at high speeds include properly designed rotating and non-rotating assemblies and bearings to support the high speed rotating shaft, typically ranging from 30,000 rpm to 200,000 rpm.
Air or water cooling may be employed to dissipate heat that is generated. However, liquid cooling has several drawbacks including additional system complexity and increased manufacturing and unit cost, and the potential for fluid leaks into the compressor/motor internals is also a concern. For the very small machines, power density is exceptional and therefore the ability to reject heat from the machines relatively little surface area becomes challenging.
Therefore, there remains a need to overcome one or more of the limitations in the above-described, existing art.
It will be recognized that some or all of the Figures are schematic representations for purposes of illustration and do not necessarily depict the actual relative sizes or locations of the elements shown. The Figures are provided for the purpose of illustrating one or more embodiments of the invention with the explicit understanding that they will not be used to limit the scope or the meaning of the claims.